Nine swing states will decide final results

After enduring 17 months of campaigning and $3 billion worth of advertising, millions of Americans will have an opportunity to vote for the next US president today.

More than 175 million US citizens are registered to vote, although polling experts believe voter turnout will be down slightly on the 55 per cent recorded in 2008 . While polls formally open today, as many as 40 per cent of the electorate have availed of early voting options over recent days or weeks.

The presidential election campaign is effectively centred on just nine swing states – one of the smallest playing fields in recent history.

Both campaigns agree that 36 states are not competitive. Some 22 will vote for Republican Mitt Romney, while 14 will plump for President Barack Obama. However the states where the president is popular are more populous. When tallied with electoral college votes attached to each state, Obama is in a stronger position.

Battleground states

These states alone with give Obama 197 votes and Romney 169. Both, then, are short of the 270 votes needed to capture the White House. No ballots have been counted yet, but several states offer information about party affiliation of the voters casting early ballots.

This data indicates that Democrats lead in four of the five battleground states, while Republicans appears to be ahead in one.

Experts have cautioned against reading too much into these findings, as final results may differ significantly.

Latest polling data indicates that President Obama carries a significant – but slim – edge over former Massachusetts governor Romney.

Democrats currently hold a majority (53-47) in the Senate chamber. One third – or 33 – of the 100 Senate seats are up for election. Republicans will need a net gain of at least three seats (or four if they fail to win the presidency) to win a majority in the Senate.

Latest polls indicate there is a much stronger likelihood of Democrats maintaining their majority.

Most observers agree there are about eight toss-up seats. Three of them have a Republican incumbent (Indiana, Massachusetts and Nevada), while five are Democratic-held seats (Missouri, Montana, North Dakota and Virginia and Wisconsin).

On the Senate side, Republican candidates in Missouri and Indiana appear to have jeopardised seats with their comments about rape and pregnancy. In Massachusetts, Democrat Elizabeth Warren now appears to have the edge on Republican senator Scott Brown. All three states are vital to the Republicans’ hopes for a majority.

One thing does seem certain is that neither side will win enough seats for a filibuster majority, which requires a 60 per cent majority.

House elections

Elections will be held for all 435 seats in the House of Representatives. If the polls are to be believed, Republicans look set to add to their majority in the House, making it the biggest in six decades.

Early on in the race, Democrats had talked about winning back a majority, but most acknowledge this is not a possibility any more.

At present, the Republicans hold 241 seats to the Democrats’ 183. A total of 218 is needed for a majority.

Polls indicate that Republicans are favoured to win as many as 10 Democratic-held seats where electoral boundaries were redrawn or where a Democratic incumbent is stepping down.

State ballots

Voters will also get a chance to back or oppose a range of issues such as the legalisation of marijuana, same-sex marriage and assisted suicide.

In all, there are 176 ballots across 38 states. Many are technical proposals related to regulations or finance, but a significant number could prove to be key social milestones in US history.

Three states – Maine, Maryland and Washington – could become the first to legalise same-sex marriage through a popular vote. This could influence Supreme Court rulings in later years.

The six states that have already legalised gay marriage did so through legislation or court orders.

Proposals to legalise the recreational use of marijuana are being put to the electorate in three states – Oregon, Washington and Colorado.

The race is particularly close in Colorado – where it is legal to use the drug for medicinal purposes – and Washington, where campaigns are backed by wealthy donors.

Election results

Voting will take place today from 11am our time (6am EST) onwards.

In previous years, US television networks have announced a winner by about 4am the next morning Irish time (11pm EST), once voting has ceased on the west coast.

The TV networks have once again pledged to abide by this principle, though some say they expect it may take much longer to pronounce a winner on this occasion, given the closeness of the presidential race.